European Patent Application No. EP 449 851 B1 describes a method for determining the amount of fuel to be supplied to an internal-combustion engine per cycle. In the known method, the stationary intake-manifold pressure is calculated from the throttle-valve angle and the engine speed. A recursion formula is applied to determine the intake-manifold pressure expected in the future.
For optimum control of an internal-combustion engine, the air charge of the cylinders of an internal-combustion engine must be known as precisely as possible, to allow metering of an amount of fuel that is adapted exactly to this air charge, and to achieve the desired torque, given low emissions and low fuel consumption. What makes it difficult to optimally meter fuel is that at the moment at which the actual air charge of a cylinder of the internal-combustion engine is known, the fuel metering for this cylinder is already complete. In other words, as a rule, obsolete air charge values are used for the fuel metering. In the case where the air charge does not change or changes only slightly from intake stroke to intake stroke, an optimal or nearly optimal fuel metering can be achieved even with the obsolete values for the air charge. During operating states in which the air charge fluctuates heavily, however, it is more beneficial to adapt the fuel metering to the air charge to be expected at any one time. To this end, a method is needed, which will make it possible to predict with the greatest possible accuracy the air charge of the cylinder into which the amount of fuel will be injected, at the time of calculation of the amount of fuel to be metered.